1. Field of the Invention
This invention relates to improvements in an airbag restraint system including a plurality of airbags which are different in an inflating manner, and more particularly to a triggering unit for initiating inflation of the airbags.
2. Description of the Prior Art
A variety of airbag restraint systems have been proposed and put into practical use for an automotive vechile. Of these, it is also known that a plurality of airbags are mounted in an automotive vehicle, in which one is disposed in a steering wheel padding for the purpose of protecting a driver seated on a driver's seat while another is disposed, for examle, in a glove box for the purpose of protecting a passenger seated on a front seat beside the dirver's seat.
Such an airbag restraint system includes a triggering unit as shown in FIG. 7. Referring to FIG. 7, the triggering unit includes a first squib 1 for igniting a first inflator (high pressure gas generator) to inflate a first airbag for the driver. Second and third squibs 2 and 3 are provided for igniting respective second and third inflators (high pressure gas generators) to inflate a second airbag for the passenger on the front seat beside the driver's seat. A capacitor 4 is provided to be charged upon raising the voltage of an electric source such as a battery 6 under the action of an auxiliary electric source circuit 5, and serves as an electric source for the squibs 1, 2, 3 when the battery is disabled upon a vehicle collision. An acceleration (or deceleration) switch 7 is electrically connected between the capacitor 4 and the squibs 1, 2, 3 and adapted to be turned ON when an acceleration (or deceleration) sensor (not shown) detects a deceleration exceeding a predetermined level.
When the acceleration switch 7 is turned ON, the charged voltage of the capacitor 4 is supplied to the first squib 1 and to the second squib 2, thereby inflating the first and second airbags. It will be understood that at this stage, the second airbag cannot be completely inflated because all the inflators have not yet ignited. Simultaneously with the turning-ON of the acceleration switch 7, a timer 8 starts clocking and causes a transistor 9 to be turned ON after lapse of a predtermined time, so that the charged voltage of the capacitor 4 is supplied to the third squib 3 thereby igniting the third inflator for the second airbag for the passenger on the front seat beside the driver's seat.
However, drawbacks have been encountered in the above discussed conventional airbag restraint system, particularly in its triggering unit. That is to say, if any one of the first and second squibs 1, 2 activated or operated prior to the third squib 3 is lowered in its resistance value below a predetermined level, an electric power consumption of the electric power source increases.